Frequency dividers are one of the most critical building blocks in wireless and wireless communication systems. They are essential in frequency synthesis, as illustrated in FIG. 1, in a typical frequency synthesizer 100, a frequency divider is used to divide the frequency down from the voltage-controlled oscillator (VCO) and generate a lower frequency signal to be compared with an input high frequency accuracy reference signal, which is normally from a crystal oscillator. With a differential-input, periodic, low phase noise signal source, both in-phase and quadrature-phase periodic differential output signals can be generated by frequency dividers with the phase noise tracking the input signal. The in-phase and quadrature-phase signals are required in zero-IF receivers for modulation or demodulation, and in image-rejection receivers such as receivers with a Weaver or Hartley architecture.
On the other hand, the evolution of the communication systems continues to move towards higher data rates, higher bandwidths and higher operation frequencies. The high frequency applications, for example, the millimeter wave integrated circuits have attracted more and more attentions recently. Building blocks in communication systems are required to operate at higher and higher frequencies while maintaining acceptable power consumption for energy saving and battery life extension. Among different types of frequency dividers, such as static frequency dividers, miller frequency dividers and the injection-locked frequency dividers (ILFDs), the resonator based ILFDs favor the highest operation frequency at the lowest power consumption. The high quality factor (Q) resonator of the ILFD can provide high impedance around the self-oscillating frequency so that only small biased current is needed for the divider to build up oscillation. However, also due to the high-Q of the resonator, the locking range of the ILFD is narrow. This further limits the applications of the ILFDs in wide band systems as well as in narrow band systems because of the process, voltage supply and temperature (PVT) variations.